Vinyl chloride-based resin is a general-purpose resin being used most extensively as living or industrial materials with olefin resins. Most of such vinyl chloride-based resins have been prepared by homopolymerization of vinyl chloride monomer. And it is being tried to develop and commercialize vinyl chloride-based copolymer resin having physical properties that could not be obtained from the vinyl chloride alone, by copolymerizing the same with various other monomers.
Polyvinyl chloride and vinyl chloride-based copolymers are being used for various purposes such as a floor material, an outdoor advertising sheet, a wall paper, or a mat. Recently, the applications to baby toys and medical purpose requiring eco-friendly property and nontoxicity to human body are increasing.
In addition, vinyl chloride grafting copolymers such as a graft copolymer of vinyl acetate and butyl acrylate are being developed for improving the productivity, and now they are being produced and on sale.
However, since polyvinyl chloride and the vinyl chloride-based copolymer resins cannot have or are lacking in softness autonomously, plasticizers such as phthalic acid esters, adipic acid esters, or phosphoric acid esters are added thereto for giving them softness. But, the vinyl chloride-based resins outer-plasticized by the addition of plasticizer show hardening property caused by migration, or extraction property by a solvent, and the range of their use is being narrowed in concert with recent environmental problems.
Furthermore, most of the vinyl chloride-based copolymers were developed for improving the thermal plasticity, flexibility, or solubility of the polymer, and most of the products developed hitherto has been used as the means for giving easy processability.
Among the vinyl chloride-based copolymers, the vinyl chloride-vinyl acetate copolymer is most widely known, and commercialized and used. The vinyl chloride-vinyl acetate copolymer has similar use to existing polyvinyl chloride resins but the cost of vinyl acetate is expensive and the content of vinyl acetate in the copolymer is insufficient to improving the processability of the final product with exclusive usage of the same.
However, there is a growing trend in the development and use of the vinyl chloride-based copolymers for the purpose of replacing the use of plasticizers which are relatively expensive and have the environmental problems disclosed above.
But, the inner-plasticized vinyl chloride-based copolymer resins having eco-friendly and excellent properties have not been developed yet.